1. Field of the Invention
The present invention relates generally to the field of separation technologies. In particular, this invention relates to separation of liquids from liquids and separation of gases from liquids. Even more particularly, this invention relates to refining of hydrocarbon liquids into fractions by distillation and/or thermal and catalytic cracking.
2. Description of the Prior Art
Prior systems for crude oil refining depend on gravitational fields for separation of oil from water and heavy admixtures from water-oil emulsion. Oil refining for fractions is carried out in the rectification columns (sometime called distillation towers), in which the separation efficiency of oil for fractions is low due to an insufficient value of the vapor pressure gradient created by the earth's gravitational field.
There are prior systems for oil refining at reduced pressure with utilization of vacuum pumps and without rectification columns, as described in U.S. Pat. No. 5,904,836 by Dae Sung Lee, et at., that permit reduction of the operating temperatures for cracking processes and improve quality of fractions separation. Here oil is heated in heat exchangers to temperatures higher than a fraction's boiling point. Then, this fraction is separated at reduced pressure in a centrifugal device from the rest of other heavier fractions, which separate light, and heavier fractions on the principle of separation of different densities by centrifugal forces. In this system, oil and water are separated in the settling volumes, which is a very slow process. There is no thermal catalytic reactor utilized in such a patent. Oil and all fractions are heated in heat exchangers to a temperature higher than a boiling point of one of the fractions. In heat exchangers, such oil heating causes appearance of a series of instabilities in the boundary between applied heat and liquid and vaporized fractions, similar to the effect which happens in heat exchangers utilized for oil vaporization in rectification columns. Also, the vacuum systems for oil refining are complex and characterized by low productivity of final products determined by the power of vacuum devices at pressures below 10−2 torr. Besides this, in high-vacuum systems the energy expenditures increase significantly for gas pumping, large dimension of vacuum pipelines, and products condensers.
In all previous oil separation systems for fractions, oil heating and evaporation that takes place in the tube furnaces require special equipment for stabilization of the boundary between the liquid-gas phases, so-called the boiling crisis, which complicates construction of the furnaces and heat exchangers, and limits vapor productivity. Standard rectification columns are bulky and have a limited lifetime of operation due to processes of chemical corrosion of their parts during interaction with sulfur, its compounds, and salts of different acids contained in oil. Gas separators for separation of oil fractions, which are made in the form of trays in the rectification columns, or centrifugal separators suggested in the above-mentioned patent are complex in construction, and have large dimensions and low productivity.
Prior systems for separation of immiscible liquids include a device called a hydrocyclone, as described in an article “The Theory and Applications of the Hydrocyclone” by Kelsal page 68-89 in the book “Solid-Liquid Separation” by Poole, et al., Chemical Publishing Company, INC., New York, 1968, and in a recent publication such as U.S. Pat. No. 5,667,686 by Schubert. These studies show that a hydrocyclone is utilized for separation of lower density liquid from a higher density liquid with a separation chamber of a conical shape with a gradual decrease in cross-sectional area throughout the entire length of the hydrocyclone. This type of separator usually has small size: a separation cylindrical section is about 10-15 cm in diameter, and the whole length is about 20-30 cm. Hydrocyclones have been in use for about two hundred years, but for the separation of liquids they have been used since early 1950's. Hydrocyclones have quite a few shortcomings such as low efficiency of separation, also inclination angles of input tubes are very critical. Small size hydrocyclones limits the separation by utilization of centrifugal forces only, and no evaporation processes or separation of liquids with different boiling temperatures were reported in experimental and theoretical studies of such devices.
There are prior systems for catalytic cracking of hydrocarbons with catalytic reactors, where catalytic reactors, as described in U.S. Pat. No. 4,664,888 by Castagnos, have substantial shortcomings such, as a difficulty in regulation of a contact time between a catalyst and a liquid hydrocarbon feedstock from about 0.2 s to 10 s, and providing a uniform interaction between catalytic particles and a liquid's volume passing through these particles. In some reactors, such as zeolitic cracking catalysis, there is high conversion activity, and it is necessary to have a contact time from 2.0 s to 5.0 s for obtaining necessary conversion, for example, of vacuum gas oil feedstock to middle distillate, gasoline, and other useful products. A contact time longer than 5.0 s of oil with catalyst which is past the optimum reaction contact time leads to excessive buildup of by-product coke on a catalyst surface and to a recracking of gasoline and middle distillate products and produces less desirable products.